test: use gotestsum to retry only the failing test

[alepane21]

Motivation and Context

We are retrying the flaking tests with a github action, that after a failure of a single test is going to retry the whole testsuite. With this PR we are using gotestsum retry instead, that is going to retry only the specific test that is failing.

Checklist

• I have discussed my proposed changes in an issue and have received approval to proceed.
• I have followed the coding standards of the project.
• Tests or benchmarks have been added or updated.
• Documentation has been updated on https://github.com/wundergraph/cosmo-docs.
• I have read the Contributors Guide.

[github-actions]

Router image scan passed

✅ No security vulnerabilities found in image:

ghcr.io/wundergraph/cosmo/router:sha-d38502c07bdf997be95710bb8fd68cc95b72e80b